The long-term objective of the proposed study is to deepen our mechanistic understanding of complex sound processing and to relate cortical neural representations to auditory perception. To this end, I propose to study complex sound processing in a central auditory circuit of a species with rich vocal communication behavior - the auditory forebrain of songbirds. Songbirds provide an excellent model for studying general principles of higher-level sound processing, because of the complex auditory tasks they face. Moreover, they possess a hierarchical network of auditory areas that subserve these tasks, including the avian equivalent of primary auditory cortex, field L. I recently found that in field there is an orderly organization of simple temporal and spectral receptive fields. This organized representation of sound features provides a framework for investigating cortical processing of complex sounds. In the proposed experiments, I will further investigate the representation at the single neuron level, by probing with natural vocalization stimuli and by mapping nonlinear receptive fields, using an information theory-based technique called maximally informative dimensions. To begin to address the circuit mechanisms that give rise to the representation, I will then map the receptive fields in field L again while selectively inactivating different subregions of field L. Finally, I will test the hypothesis that field L subregions with different tning properties differentially contribute to perception of complex sounds, by inactivating subregions of field L while birds perform operant song discrimination tasks. The outcome of the proposed study will not only further our basic understanding of how spectrotemporal receptive field arise through neural circuits and how they relate to perception, but will also have important implications for treating auditory disorders.